Thermostat



April 1942- F. DRAKE 2,279,305

THERMOSTAT Filed Jan. 1'7, 1938 2 Sheets-Sheet l INVENTOR e Forrest Bra/(e ATTORNEY$ April 14, 1942. G. F. DRAKE 2,279,305

THERMOSTAT 2 SheetsSheet 2 Filed Jan. 17, 1938 Patented Apr. 14, 1942 THEBMOSTAT Rockford, 111., assignor to Barber-Colman Company, Rockford, 111., a cor- George Forrest Drake,

poration of Illinois Application January 17, 1938, Serial No. 185,388

ilClaim.

This invention relates generally to condition control instruments such as thermostats and more particularly to those of the bimetallic type which are adapted to be mounted on the wall of a room and utilized to control an apparatus for changinz the temperature 01 the room air. The general object o! the invention is to provide a room thermostat substantially greater speed of response to ambient temperature changes than prior room thermostats.

A more detailed object is to correlate the construction and podtion oi the bimetallic element the thermostat with the room environment so that the natural circulation of air inherently occurring in the room being conditioned may be u advantage in increasing the sensitivity of the thermostat.

Another object is to provide a thermostat having control switches of the open'contact type protected in a novel manner a contact surfaces by dust particles.

A further object is'to provide, in a thermostat tion of the adjusting mechanism therefor.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment. It is to be understood, however, that I do not intend to limit the invention by such disclosure but aim to cover all modifications and alternative constructions falling within the spirit and scope or the invention as expressed in the appended claims.

Referring now to the drawings, the improved room thermostat II is mounted on a wall ll of a room and arranged-to control the operation of an tilinedtohl gainst iouling of the apparatus for changing the temperature of the air The apparatus may, for exl! supplied with temperature changing medium under the control ota' valve it which is actuated by a power drivenoperator ll controlled irom the thermostat through the medium of connections indicated at II and extending between the thermostat and the valve operator.

In the present instance, the thermostat is of the electric type comprising generally a strip I! of bimetallic material adiustably supported from one end and carrying at its free ends contact ll having oppositely lacing surfaces II and il which cooperate with stationary contacts 2. to form electric control switches 2| and 2!. The thermostatic element and the contacts as well as the Other objects and advantages of the invention will become apparent from the following detailed descri tion taken in connection with the accompanying drawings, in which Figure l is a fragmentary perspective view oi a room and temperature chand m apparatus controlled by a thermostat embody d the novel lestures oi the present invention.

Fig. 2 is a perspective view oi the thermostat. Fig. 3 is a vertical Fig. 4. is a nagmentary perspective view at the main operating parts.

Fig.5isancflcntakenahngthe line 8-4 0! Fig.6.

Pig. 6 is a section takmalong the line H c! alongthelineHoiFigJ.

Fig. 10 is a section taken along the line IF" I 0! Fig. 5.

sectional view taken approximately on'the line 8-4 of Fig. 5. i

other operating parts of the instrument are mounted on a base 23 of molded insulation which cooperates with a removable and generally rectangular cover 24 to form a casing for the operattree circulation of the room air through the a. wall of the room usually on the side opposite the changer or the point of discharge medium into the room. disposed in the natural path of circulation or the room air which has been found to movevertlcally along and adjacent the suriau of the wall or any other vertical surface of relatively large area. The present invention aims to take advantage 0! this condition and utilize the same in obtaining optimum speed of response of the thermostat to ambient temperature changes. To this end, the bimetallic strip I is made substantially straight and flat with a relatively large ratio of surface area to volume of the metal and is mounted in the upper part of the casing in a substantially horizontal plane when the casing is attached to the wall in the intended position.

The strip is thus disposed broadwise to the direc= ing post 62 rigid with the adjusting slide 43. tion of current oi air which moves downwardly Thus, the scale reading in degrees indicates the through the casing as indicated by the arrows in position of the slide it and therefore the ambient municated quickly to the metal or the strip positions of the blocks 50 which act as limit stops The desired large ratio of surface area to and cooperate with shoulders 64 on the slide 43 volume 01' bimetallic material used is obtained b It will be observed that the pivot 35 about is approximately twiceasgreat, about thirty-four the supported end of the latter. By virtue of in the present instance, a the ratio commonly such arrangement coupled with the location of used in the construction of prior room thermo- 5 the pivot close to the strip, the reduction in the stats. eii'ective wldth'of the air gap between the switch The high sensitivity of the present thermostat contacts due to curvature of the strip under is also due in part to the fact that the strip I 6 temperature changes and changes in the thermois disposed with the metal layer ll (Fig. 9) of stat setting is decreased substantially. higher expansibility facing upwardly. Thus, he stationary contacts 20 are carried on the changes in the temperature of the downwardly ends of screws 85 threading into posts 66 which the pivot i t d 36 plvotally supporting a assembled thermostat, the cover mold bears lever 31 which has a lug 38 thereon bearin against the end oi the dust housing and holds the against the end of a adjusting Screw 39 t latter against the base (see Fig. 7). The housmovement The bar slides in a slot 4: (Fig 8) 5e m of the pa as a n dent to ssemb in y in the base 23 and has oppositely projecting lugs the he m ta casing is avoided I and 45 formed thereon and cooperating with t particles which do settle on the upper guides 48 and 41. The bar is held against th surface of the thermostatic strip exterlor'ly of base by overlying flanges 49 on blocks 50 which the hou ing are preven ed from creeping along are adjustable along slots 5| in the base and e strip and o he up er rface It or the clamped against the latter by screws 52 (Fig. 4) contact T s is accomplished y p g t s threading t t blocks 7 contact surface abovethe strip with its outer An arm 53 rigid with the slide bar 43 projects e iphery overl ng e Strip 0 .8 to form an downwardly through a slot 54 in the cover 24 and annular Docket 8 ny-pa t c es which constitutes a handle by which the bar may be 0 cr ep along the strip will collect and he re-;

' Docket.

construction much more sensitive to changes in the ambient temperature room thermostats heretofore used.

The inner ends of the posts whic project through the base 23 are threaded and provide terminals on the rear side of the base to which lead-in conductors may be attached. The connection with the common switch contact 11 is through a short end portion of the strip I] and a very flexible conductor 13 having one end soldered to the under side of the strip near the free end thereof so that the current carried by the thermostat switches will not flow through any substantial length of the bimetallic strip and the base 23 near the fixed end of the strip It and providing the third terminal on the rear side of the base. The conductor ll is a fine braided wire which in view of its extreme flexibility and the fact that it extends substantially parallel to the strip imposes substantially no force on the strip throughout the range of movement of the latter. In addition, the arrangement avoids any possibility of contact with the metal parts.

Both metals of which the thermostatic strip it is composed are of the magnetic character. Advantage is taken of this property and the strip itself is utilized to perform the additional function of constituting the armature of a magnet for causing movement of the common switch contact with a snap or detent action. Herein, the magnet comprises two alined pole pieces 15 of permanently magnetized material supported in a yoke 18 which is fastened to the base 23. The opposed pole faces 11 are disposed in parallel planes and spaced apart so that the gaps between the pole faces and the armature surfaces are somewhat wider than the range of movement of the switch contact II. The contacts 20 are adjusted so that the strip I8 is disposed on the magnetic center of the gap between the pole faces than the bimetallic sons, the base I and the cover 24 are, after adiustment of the thermostat and the thermometer at the factory, secured together by screws 08 (Fig. 6) extending through the base and the threading into metal inserts I'l molded into the cover. The screw heads are seated in recesses as which may, if desired, be sealed. The as sembled thermostat is fastened on the room. wall by screws '8 (Fig. 10) extending through the cover and base and having heads llil seated in the cover and concealed beneath ornamental band ill. The latter is apertured to receive plugs I02 formed integral with the cover and acting to secure the band against the cover with a snap fit.

Means is provided for insuring accurate positioning of the adjustment indicator II and the scale 51 when the base 23 and the cover 24 are assembled in spite of inherent manufacturing variations in the dimensions of the molded parts. To this end, the periphery of the cover is made somewhat larger than the base I! so as to fit loosely over the latter. A dowel plug in (Fig. 6') is molded onto the base around the screw hole which is adjacent the indicator H and this dowel is adapted to flt" snugly into a recess Ill on the cover and thereby locate the cover laterally of the base during assembly of the two. Since the dowel and recess can readily be molded to fit accurately and are disposed close to the indicator ii and the scale 51, the effect of manufacturing variations on the accuracy of the adjustment when the contact I1 is midway between the con-v tacts 20.

The thermostat may be equipped with an auxiliary electric heater .0 which preferably comprises a resistance coil wound on an insulating spool I. The latter is fastened by a bolt 82 tothe forwardly projecting arms of L- shaped brackets I3 secured to the base I! by screws 84 and insulated from each other. Op-

*posite ends of the coil are connected to the brackets the screws of which provide electrical terminals on the rear side of the base. I A constant indication of the ambient temperature is given by a thermometer I! concealed within the thermostat casing with its scale 81 visible through a window 88 in the front wall of the cover. The scale is formed on the bar 6! and oooperateswith a column '8 (Figs. 6 and 8) of expansible fluid in a horizontal glass tube N which is mounted in and substantially enclosed by an insulating member 00 slidable along the rear surface of the cover wall ii. In this movement the member is guided by a rib 82 (Fig. 3) on the cover entering a groove 9| in the member, the latter being fastened to the cover by a screw 88 after calibration of the thermometer.

The bulb N of the thermometer is disposed within a recess is (Figs. 2 and 6) in one side wall of the cover and opening outwardly. The bulb is thus exposed to the air exteriorly of the thermostat casing and is effectively insulated against heating by radiation from the electric heater II.

To discourage tampering byunauthorized perreading will be reduced to a minimum.

I claim as my invention:

1. A thermostat adapted to be mounted on the wall of a room and having a horizontally extending contact carrying element movable vertically in response to ambient temperature changes, a contact cooperating with the contact of said element, a housing enclosing said element and apertured for the circulation of air therearound, a closure within said housing around said contacts and one end portion of said element, and means within said housing operable to prevent dust particles settling on said element exteriorly of the housing from creeping along the elementand onto the active surfaces of said contacts.

2. A room thermostat having, in combination, a support adapted to be secured to the wall of a'room, an elongated arm supported at one end from said support and disposed substantially horizontally when the thermostat is mounted on said wall, the free end of said arm moving vertically in response to ambient temperature changes, a housing enclosing the free end portion only of said arm, and an electrical contact carried by said free end within said housing and providing an upwardly facing contact surface disposed above the upper surface of said arm 50 as to prevent dust particles on the latter creeping into said housing along the upper surface of said arm from coming onto said contact surface.

3 A room thermostat having, in combination, a support adapted to be secured to the wall of a room, an elongated arm supported at one end from said support and disposed substantially horizontally when the thermostat is mounted on said wall, the free end of said arm moving vertiof said arm so as to prevent dust particles on the latter from creeping onto said contact surface,

closure around said conand means providing a tact and operating to prevent dust particles from settling thereon.

4. A thermostat adapted to be mounted on the wall or a room and having a horizontally extendlng contact carrying element movable vertically in response to ambient temperature changes, a contact cooperating with the contact of said element, a casingenclosing said element and hav- 6. A condition respon ive instrument having, in combination, a base; a perforated cover telescoping loosely with said base and ooperating therewith to define a chamber, a-coudition re- -7. The combination witl: apparatus for chanzin: the temperature or the air in e room having a relatively large vertical wall surface 01. a then moatat having a thermosensitive element com-- prising an elongated thin and substantially flat strip 01' bimetallic material and a hollow casing GEORGE FORREST 

